The present invention relates to a sensor and guide wire assembly for intravascular pressure measurements having improved handling properties in the vessels in which it is to be inserted.
A sensor mounted on a guide wire suitable for use in intravascular pressure measurements is disclosed in International Patent Application No. WO 90/01294 and in U.S. Pat. No. Re. 35,648, and U.S. Pat. No. 5,715,827. One known sensor and guide wire assembly comprises a core wire having segments of varying thicknesses in at least the distal region of the core wire. In situations where it is desirable to attach a sensor having electrical leads connected thereto to the core wire, the core wire is enclosed in a tube, and the electrical leads run parallel inside the tube along the core wire. The core wire may, but need not, extend all the way to the proximal end of the tube. If the sensor is a pressure sensor, it is preferable to provide some sort of stiffening member for the sensor in order to avoid mechanical artifacts due to, for example, bending. It is known to provide a short, protective tube segment enclosing the sensor to stiffen and protect the sensor region of the guide wire. A stiffening member of this type has several limitations, however.
A first drawback of a protective tube segment, of the type indicated above, is that the formation of a joint between the coils and protective tube segment is difficult to make, and mismatch often occurs between coil and tube. Put another way, it is difficult to obtain good concentric matching.
A second drawback of a protective tube segment relates to the manufacturing process, which becomes more complicated because an additional structure, i.e., the protective tube segment, must be assembled as part of the sensor and guide wire assembly. A conventional means of attaching the protective tube segment to the sensor is with glue or another suitable adhesive, but this attachment method renders the joint non-optimal from a mechanical point of view. Further, the thermal expansion coefficient of the adhesive may differ from that of the materials used in the remaining components of the sensor and guide wire assembly, which can cause problems. The protective tube segment also makes the sensor region relatively stiff, and the length of the protective tube segment cannot be made as short as desirable.
A third drawback of a protective tube segment is that the tube segment constitutes an asymmetric and non-flexible or stiff portion that hinders bending at turns in a vessel.
A fourth drawback of a protective tube segment is that the inner diameter of the tube segment puts limitations on how the segmenting of the wire can be achieved.
The difficulties suggested in the proceeding are not intended to be exhaustive but rather are among many which tend to reduce the effectiveness and manufacturing efficiencies of conventional sensor and guide wire assemblies. Other noteworthy problems may also exist; however, those presented above should be sufficient to demonstrate that such assemblies appearing in the past will admit to worthwhile improvement.